Process and composition for coating electrodes



Patented Sept. 25, 1934 e a ELECTRODES I Eugene 1A. Giard, S horewood,Wis., assignor to porationfof Delaware Electron dfisch'arg'ftubes are"frequently equipped with cathodes which arefcoated'with emissionfincreasing-*materials "such as barium h oxide and strontium."Therriethods of coating dsuoli electrodes employed heretofore are verycumbersome andresult'frequentlyin failures due to the difficulty offcausing'f-the oxides to adhere *to'thesurface of theelectrodes, I

,With the methodsfheretofore used itisciis- 10 tornarytostart witha-desire'd mixture of barium carbonate and strontiumcarbonate to whichare frequently added bariuin nitrate and/or strontiurn nitrate andsometimes small, quantities of various organic substances." ,Thesematerials are put into a ball mill together "wi tli a sufficient amountof water to form a slurry of proper consistency, the slurry beingprocessed in the mill for a prolongedperiod offrom 12'to 20 hours. "Thecathodes are'then giyen'sever'alcoats of the slurry and baked after eachcoating at an elevated temperature in anfatmosphere of carbon dioxide.

- The, coatingmixture ere theelectrode surface f only with diflicultydueto its large surface tension faceandto prevent small bubbles.The'ball- "milling operation usuallyresultsjin the formation verydiflicult to break downj and thelsmall bubb'les thereof; if allowed to'rach "the Su -race of the electrode, result in'baref spots and areasof'unequalco'ating density. "As a result the final coathandling of thecathode particularly if the latter is of filamentary form and has to bebent after processing. The baking temperature must also be carefullycontrolled as too low a temperature 40 produces insufficient adherenceof the coating,

while too high a temperature causes it to sinter on the surface of theelectrode and to crack when the electrode is bent.

The present invention has for its object to provide a method of andmeans for coating electrodes which will be free from the aforementioneddisadvantages.

Another objeot of the invention is to provide a method of coatingelectrodes which produces a tenaciously adhering coating.

Cutler-Hammer, Ino., ltfitilwaukee, Wis., a corwill not crack off theelectrode upon the moderate "bending of the latter.

"are dissolved in ethylene glycol.

as a decomposition accelerator, thus eliminating the necessity of addinga separate agent for this "purpose as is the case with other methods.

and has a tendency to collectinto beads on the of alfoam on'the surfaceof the slurry which is ing'is unev'emandflakes 01f during subsequent NoDraWing. Application December 10, 1931,

Serial No. 580,226

(oi. as -21.5)

Other objects and advantages will hereinafter appear.

'Wi'th my present method approximately equal C30 quantities of bariumoxide and strontium oxide It is known at the present time whether thisforms a true solution or whether the glycol forms compounds with thebarium and strontium. This property ".65 of the glycols and relatedcompounds may be analogous tothe well known property of sugar solutionswhichtake hydrates of these elements into solution. Indeed, as is thecase with sugar solutions, it is impossible to precipitate all the 7pybariu and strontium with carbon dioxide. Further, it was found that asmall quantity of the solvent or the compound remains in the completedcoating, as will be described later, and acts The solution containingthe barium oxide and strontium oxide is next heated to boilingternperature (197 C.) while carbon dioxide gas is passed through it.This causes precipitation of substantially all of the barium andstrontium in the form of their carbonates. The latter are in a veryfinely divided condition and are thus well suited for the coatingoperation. By regulating the temperature of the solution and the rate ofthe addition of the carbon dioxide gas, it is possible to regulate theparticle size within wide limits. The ball milling for securng smallparticle sizes used with other methods as afore-' described is thusobviated.

I have found that barium nitrite and strontium nitrite are easilysoluble in glycols. In the present process I preferably dissolve a smallquantity of barium nitrite in ethylene glycol and mix the resultingsolution with the aforedescribed solution of barium carbonate andstrontium carbonate at the boiling temperature of the glycol and stiruntil all evolution of gas ceases. While the exact function of thebarium nitrite is not known, it presumably acts as a binder and it hasbeen found to be very beneficial for the production of a good coating.

The resulting composition or slurry of barium nitrite in solution andbarium carbonate and strontium carbonate in suspension in ethyleneglycol is next applied to the cathode while hot. The slurry flows freelyand wets the metal surface very readily having a tendency to spreadthereon. Thereafter the ethylene glycol is evaporated in an atmosphereof carbon dioxide at a temperature of approximately 200 C., suchtemperature not being critical. By suitably adjusting the ratio ofsolids to liquids, it is possible to apply in a single coating astrongly adhering deposit of emission increasing material which is ofequal efficiency to a coating applied in accordance with anotherfrequently used method, but which to obtain equal adherence requiresthat the coating be applied by about nine successive applications.

The coating produced by the present method is far superior to thecoating obtained by the older methods in that it adheres better to thecathode and is more readily decomposed at elevated temperatures. Thus,for instance, a thin ribbon coated by the new method Was wound in theform of a spiral on a one-eighth inch mandrel thereafter removed andstraightened and then Wound on the same mandrel in the oppositedirection Without losing an appreciable quantity of the coating. Withthe methods used heretofore such a treatment would have resulted in theremoving all or" the coating from the ribbon.

It should also be pointed out that the temperature to which the materialhas to be heated for conversion from the carbonates to the oxides isconsiderably lower than that which has to be employed with the olderprocesses. This lower temperature requirement is probably due to theextremely small size of the barium carbonate and strontium carbonate,and the presence of a small amount of carbon which remains from thedecomposition of the organic material, and which is known to bebeneficial for this purpose.

This invention is not limited to the use of ethylene glycol. Severalother glycols with both primary and secondary alcohol radicals have beenfound satisfactory as have also certain polyhydric alcohols. Forinstance, a mixture of ethylene glycol and glycerine has been found anexcellent means of introducing additional carbon into the coating topromote the decomposition of the carbonates to the oxides. Theglycerine, a tri-hydric alcohol, can be used alone and functions in amanner similar to the glycols. It obviously becomes possible to producecoating mixtures with widely varying physical and chemical properties bya suitable choice and blending of the various members of the glycol andpolyhydric alcohol families. Thus wherever I use the term glycol in theappended claims, it is to be understood to cover any or all of theaforementioned substances.

It is also possible to use barium compounds or strontium compounds aloneor use them in any suitable mixture. Wherever the term barium is used inthe claims, it is to be understood that it is also to cover thecorresponding strontium compound or a mixture of both compounds.

What I claim as new and desire to secure by Letters Patent is:

- 1. An electron emission increasing coating consisting of a glycol basecontaining soluble salts of barium, colloidal barium carbonates, andbarium compounds with the glycol.

2. An electron emission increasing coating containing the mixtures ofbarium carbonate with a glycol.

3. An electron emission increasing coating which consists of a mixtureof barium carbonate with a glycol and other barium and strontium salts.

4. The method of producing an emission increasing coating mixture whichconsists in precipitating barium carbonate from a solution of bariumoxide in a glycol by carbon dioxide and adding a solution of bariumnitrite in a glycol.

5. The method of producing an emission increasing coating mixture whichconsists in precipitating barium carbonate from a solution of bariumoxide in a glycol by carbon dioxide under application of heat and addinga solution of barium nitrite in a glycol.

6. The method of producing an emission increasing coating mixture whichconsists in precipitating barium carbonate from a solution of bariumoxide in a glycol by carbon dioxide and adding a solution ofbariumnitrite in a glycol, applying the mixture to the surface in anatmosphere of carbon dioxide and evaporating the volatile constituents.

'7. The method of producing an emission increasing coating mixture froma solution of barium oxide in a glycol which consists in precipitatingbarium carbonates by carbon dioxide and adding a solution of bariumnitrite in a glycol, applying the mixture to the surface in anatmosphere of carbon dioxide and evaporating the volatile constituentsat an elevated temperature.

8. The method of producing an emission increasing coating mixture from asolution 01' barium oxide in a glycol which consists in precipitatingbarium carbonates by carbon dioxide, adding a solution of barium saltsin a glycol and applying the mixture to the surface while maintainingthe latter at an elevated temperature to rapidly evaporate the volatileconstituents.

EUGENE A. GIARD.

CERTIFICATE OF CORRECTIQN.

Patent No. 1,974,608. September 25, 1934.

EUGENE A. GIARD.

It is hereby certified that error appears in the printed specificationof the above numbered patent requiring correction as follows: Page 1,line 62, before "known" insert the Word not; and line 89, for "securng"read securing; and that the said Letters Patent should be read withthese corrections therein that the same may conform to the record of thecase in the Patent Office.

Signed and sealed this 12th day of February, A. D. 1935.

Leslie Frazer (Seal) Acting Commissioner of Patents.

